The Secret Service said a foreign government leader might reconsider how he interacts with agency bodyguards on visits to the United States in light of a judge's ruling that agents can be forced to testify in a grand jury investigation of President Clinton.

The leader told agency Director Lewis C. Merletti that he fears his privacy could be jeopardized if agents can be ordered to say in court what they witness, Secret Service spokesman Arnette Heintze said yesterday.

Heintze would not identify the leader, except to say that he is "head of a G-7 country," or leader of one of the world's richest industrialized nations. Newsweek magazine reports in its issues on newsstands today that the leader is Canadian Prime Minister Jean Chretien.

Citing unidentified sources, the magazine said a top Chretien aide relayed his boss's concerns to Merletti at a January meeting. In an affidavit filed in independent counsel Kenneth W. Starr's investigation of Clinton's relationship with former White House aide Monica S. Lewinsky, Merletti said unsolicited concerns about privacy had been raised by an unidentified foreign head of government.

Heintze declined to speculate on whether other world leaders might have a similar reaction, but said, "Somebody has to weigh this issue very cautiously, because political assassinations are a way of life."

Clinton predicted last week that the ruling would have "a chilling effect" on the way presidents conduct themselves around their bodyguards. In the ruling, Chief U.S. District Judge Norma Holloway Johnson said Secret Service agents could not remain silent about the president's activities if called to testify.

She said agents have testified voluntarily in some previous cases and she was "not convinced that compelling Secret Service personnel to testify before a grand jury regarding evidence of a crime would place presidents in peril."

"We would have less trust and confidence from the protectee and be pushed out, a couple of feet to a matter of yards," Heintze said. "We think that history has shown that proximity has been, definitely, a factor in previous assassination attempts on presidents, and tragically, the death of a president."

Timothy J. McCarthy, the Secret Service agent wounded in the 1981 assassination attempt on President Ronald Reagan, said on NBC's "Meet the Press" yesterday that the judge's ruling threatens the already difficult relationship between agents and foreign leaders.